Maritime tropical (mT) air is observed only infrequently on the Pacific coast, particularly near the surface. Air flowing around the northern boundary of the Pacific anticyclone is at times mT air but is usually mP air. This air has the weather characteristics (as well as the low temperature) of mP air, having had a long trajectory over the water. (See fig. 4-1-9.)

Occasionally the eastern cell of the Pacific an-ticyclone splits, and one portion moves southward off the coast of southern California. This portion

Figure 4-1-9.Trajectory of mT air over the Pacific in winter.

of the anticyclone is then able to produce an influx of mT air. Generally the influx of mT air is carried aloft by a rapidly occluding frontal system somewhere over southern California, pro-ducing the heaviest precipitation recorded in that area. Occasionally mT air is seen above the sur-face with pronounced storm developments over the Great Basin. Since large, open, warm sectors of mT air do not occur along the west coast, representative air mass weather is not experienced. Flying conditions are generally restricted when this air is present, mainly because of low frontal clouds and reduced visibility in precipitation areas.

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